USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Wildlife & Fish

Invasive Species

Research by PSW scientists demonstrates that introduced trout and other species have caused major changes in abundance and distribution of native amphibians, zooplankton, and benthic invertebrates, changes likely to result in federal endangered species listings. Scientists are looking at the impacts of introduced fishes on invertebrates, amphibians, reptiles, birds, and bats.

One example is the Sacramento pikeminnow, a native of the nearby Sacramento-San-Joaquin drainage, is the invasive fish of interest in the Eel River, primarily because of its propensity to consume fish, including salmonids, and its broad distribution in the invaded system. Research by USDA FS PSW scientists has revealed that predation on salmonids by pikeminnow is localized, but that competition among juvenile pikeminnow and salmonids may also be significant. Further research has revealed that eradication of this invasive species is not feasible but the importance of water temperature to the interactions between pikeminnow and salmonids indicates that management actions focused on shifting parts of the system toward cooler, historic thermal regimes could significantly reduce the influence of invasive fishes on native salmonids.

Publications on the pikeminnow from TreeSearch
Date Title Author
2002 Habitat relationships and larval drift of native and nonindigenous fishes in neighboring tributaries of a coastal California river Harvey, Bret C.; White, Jason L.; Nakamoto, Rodney J.
2002 Temperature-dependent interactions between juvenile steelhead and Sacramento pikeminnow in laboratory streams Reese, Carl D.; Harvey, Bret C.
2001 Effects of an introduced piscivorous fish on native benthic fishes in a coastal river White, Jason L.; Harvey, Bret C.
1999 Diel and seasonal movements by adult Sacramento pikeminnow (Ptychocheilus grandis) in the Eel River, northwestern California Harvey, Bret C.; Nakamoto, Rodney J.

Trout are not native to most high elevation ecosystems and have been extensively used to stock lakes for recreational fishing, including the Sierra Nevada and Klamath-Siskiyou Wilderness Areas. According to Executive Order 13112, an "invasive species" is defined as a species that is 1) non-native (or alien) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

Considerable published information now exists to demonstrate that non-native trout have caused environmental harm to high elevation aquatic ecosystems. PSW studies have demonstrated that trout have caused major changes in abundance and distribution of native amphibians, zooplankton, and benthic invertebrates, changes likely to result in federal endangered species listings. Moreover, amphibian declines caused by trout introductions have also lead to declines in predators (example: the mountain garter snake, the only snake native to high elevation ecosystems), thus trout introductions have resulted major disruption and cascading effects throughout the ecosystem.

When trout are not native to aquatic ecosystems, and their introductions result in major environmental changes, they can be considered invasive species. Future work must include developing ways to manage fish stocking to minimize deleterious effects and restore native species.

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Klamath-Siskiyou Bioregion

High Mountain Lake Fish Stocking Studies

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